高耸桥墩保护性爆破拆除关键技术

为解决高耸钢砼桥墩上部倾斜导致的工程质量不合格问题,采用保护性控制爆破将上部倾斜部分钢砼桥墩予以拆除,同时保留下部未偏斜部分桥墩不受破坏。采用开设组合形状切口,预开定向窗、导向窗;设置组合高差卸荷槽,预伤钢筋弱化抗压抗拉能力为关键措施的控制爆破方案。方案实施取得了十分满意的效果,上部拟拆除部分桥墩顺利倾倒下坠,下部保留部分桥墩完好无损。采用保护性控制爆破技术能高效、安全地解决类似高耸钢砼桥墩(构筑物)部分拆除、部分保留利用的问题,并能取得可观的经济、社会效益。     

基于介形类生态特征评价湖南某铀矿山地表水放射性环境

湖南某铀矿为我国一重要铀资源生产基地，长年的矿冶活动使该铀矿冶地域生态环境不可避免地遭到了一定程度破坏。本文以该铀矿冶地域介形类为研究对象，分析其分布与生态特征，并利用该生物评价本矿冶地域地表水放射性污染状况。结果表明，Cypridopsis vidua在溪流与河流中均有分布，Helerocypris incongruens仅发现于河流，两者丰度均不高。利用该两种介形类丰度及总丰度变化可指示水体铀浓度的变化，丰度越小，铀含量越大，反之亦然。Shannon-Wiener物种多样性指数与水体铀浓度呈明显负相关，表明也可利用介形类生物指数指示水体铀浓度。该生物指数明显偏低，说明该铀矿冶地域地表水环境质量需要改善，放射性污染应引起足够重视。     

A comparison of manual handling risks in different domestic waste collection systems using three separate evaluation methods

Arising out of the challenge for Local Authorities (LAs) to operate sustainable systems of work, is to avoid the creation of ill-health including the most significant causes of physical absence, musculoskeletal disorders (MSDs).The study's aim was to compare the reliability of the manual handling element of the Health and Safety Executives (HSEs) risk comparator tool for different domestic waste collection methods with self-reported pain via body-mapping and MSD ill health absence rates. Participatory body-mapping exercises were carried out in five LAs with one LA resurveyed, six months after the move from 35 and 50 L containers to a wheeled bin recycling service.The lowest levels of self-reported pain were for services designed with 240l wheeled bins excluding glass; the highest levels were for services that included 100l of garden waste sacks and recycling boxes. Industry data supports previous laboratory studies showing wheeled bins to be associated with less MSD outcomes than boxes, baskets and sacks.Triangulation of data established a statistically significant correlation of 0.85 (Pearson) between average pain-count (APC) and the mean MSD absence rates, with a strong correlation of 0.77 (Spearman) between APC and risk rating. The correlation is moderate, 0.49 (Spearman) between MSD absence and risk rating, reflecting possible intervening variables and a low participation rate by LAs.The contribution of this study is to improve the design of sustainable waste collection strategies to minimise MSD associated absence. In the absence of reliable absence data, body mapping should be used as a proxy method of assessing MSD risk.     

Digital twin-based assembly data management and process traceability for complex products

Complex products such as satellites, missiles, and aircraft typically have demanding requirements for dynamic data management and process traceability. The assembly process for these complex products involves high complexity, strong dynamics, many uncertainties, and frequent rework and repair, especially in the model development stage. Achieving assembly data management and process traceability for complex products has always been a challenge. A recently proposed solution involves one-to-one mapping of the corresponding physical entity, also known as the digital twin method. This paper proposes a digital twin-based assembly data management and process traceability approach for complex products. First, the dynamic evolutionary process of complex product assembly data was analyzed from three dimensions: granularity, period and version. Then, a framework of digital twin-based assembly data management and process traceability for complex products was constructed. Some core techniques are: 1) workflow-based product assembly data organization and version management; 2) synchronous modeling of the product assembly process based on digital twin; and 3) hierarchical management and traceability of product assembly data based on digital twin. On this basis, an algorithm flowchart for generating a product assembly data package was created, which includes product assembly data management, assembly process traceability, and generation of a product assembly data package. Furthermore, the Digital Twin-based Assembly Process Management and Control System (DT-APMCS) was designed to verify the efficiency of the proposed approach. Some aerospace-related assembly enterprises are currently using DT-APMCS and achieving satisfactory results. Finally, a summary of our work is given, and the future research work is also discussed.     

A mechanism informed neural network for predicting machining deformation of annular parts

Controlling machining deformation of annular parts is crucial for ensuring the performance of high value products and equipment. For example, during manufacturing of critical parts in aircrafts and spacecrafts, accurate prediction of machining deformation is the basis for guiding the formulation of deformation control strategies. However, due to the complexity of the machining deformation of annular parts, existing methods still have limitations in accurate prediction. To this end, this paper proposes a mechanism informed neural network (MINN) to predict machining deformation of annular parts. MINN is realized by establishing the dual sub-networks structure and using enhanced loss functions with the consideration of the deformation mechanism model characteristics of annular parts. The deformation was decomposed into the axisymmetric portion and the non-axisymmetric portion according to the deformation superposition principle, and modeled separately based on the thin-shell theory and Fourier series. Experiment results showed that the proposed method could predict the machining deformation of annular parts more accurately and stably with a small amount of training data, compared with previous methods.     

Context enabled decision aids to support the situation awareness and performance of risk engineers carrying out loss prevention surveys

Routine inspection by insurance companies at their clients’ facility, also known as loss prevention survey, help identify the best strategies to minimize damages when there is a high-speed wind event. More specifically, wind vulnerabilities associated with a building are evaluated using a process known as windstorm risk inspection. This routine inspection helps clients reduce the extent of damages caused by high-speed wind events including hurricane and tornado. Risk engineers make use of their subjective and analytical deduction skills to successfully carry out the inspection tasks. In this research the researchers investigated the effect of context-based visualization strategies on situation awareness and their understanding of the situation. The study examined how different types of information contribute towards the three levels of situation awareness. Following a between-subjects study design, 65 participants completed the study. Each session lasted 90–120 min. A checklist based and predictive display-based decision aids were tested and found to be effective in supporting the situation awareness requirements as well as performance of risk engineers. However, the predictive display only helped with certain tasks such as understanding the interaction among different components on the rooftop. For remaining tasks such as perceiving obvious issues like membrane tear, clogged drains and vegetation growth, checklist alone was sufficient. This study helped the understanding of the advantages and disadvantages of the decision aids tested. More specifically, these decision aids can improve the mental model of novice risk engineers. Additionally, this study provided insights that could help design training materials for infrastructure inspectors.     

Perovskite ceramic oxide as an efficient electrocatalyst for nitrogen fixation

The electrochemical conversion of N₂ to NH₃ is an interesting research topic as it provided an alternative and energy-saving method compared with the traditional way of NH₃ production. Although different materials have been proposed for N₂ reduction, the use of defects in oxides was only reported recently and the relevant working mechanism was not fully revealed. In this study, Sr was used as the dopant for LaFeO₃ to create oxygen vacancies, forming the Sr-doped LFO (La_0.5Sr_0.5FeO_3-δ) perovskite oxide. The La_0.5Sr_0.5FeO_3-δ ceramic oxide used as a catalyst achieves an NH₃ yield of 11.51 μgh^?1 mg^?1 and the desirable faradic efficiency (F.E.) of 0.54% at ?0.6 V vs reversible hydrogen electrode (RHE), which surpassed that of LaFeO₃ nanoparticles. The ¹⁵N isotope labeling method was employed to prove the La_0.5Sr_0.5FeO_3-δ catalyst had the function of converting N₂ into NH₃ under the electrolysis condition. The first principle calculations were used to investigate the mechanism at the atomistic level, revealing that the free energy barriers changed significantly with the introduction of oxygen vacancies that accelerated the overall nitrogen reduction reaction (NRR) procedure.     

预应力锚索锚固力监测点经济高效布设方法研究

预应力锚索锚固力监测点合理布设是提高边坡稳定性监测可靠性的重要手段，在确保边坡稳定安全的同时，可最大程度上节省工程监测成本。现阶段预应力锚索锚固力监测点布设方案设计多依赖工程经验，具有很强的盲目性并且监测成本较大，尤其对于大型高陡边坡，由于挖方量和边坡加固工程量巨大，如何实现高陡边坡预应力锚索锚固力监测点经济高效布设，保证边坡安全高效监测是目前亟需解决的问题。以广东省江门市迎宾西路某高边坡为研究背景，通过研究锚索的群锚效应和锚索失效后的影响范围，确定了监测点之间的合理布设间距。构建了边坡三维模型，通过数值计算，模拟高边坡开挖全过程，由数值计算结果分析边坡开挖过程中变形失稳的潜在危险区域，进行监测点选择型布设。通过上述方法，实现了该段高陡路堑边坡预应力锚索锚固力监测点的经济高效布设。研究表明：基于群锚效应与三维数值模拟方法，提出的预应力锚索合理布设间距与开挖过程中潜在危险区域重点监测相结合的综合布设优化方案，可合理利用材料和空间、大幅节省监测成本，实现边坡的经济、高效监测。研究成果为高陡路堑边坡稳定性监测点合理布设提供了一种新的思路。     

Safety analysis of reactivity insertion accidents in a heavy water nuclear research reactor core using coupled 3D neutron kinetics thermal-hydraulic system code technique

Nuclear power plant Safety analysis using coupled 3D neutron kinetics/thermal-hydraulic codes technique is increasingly used nowadays. Actually, the use of this technique allows getting less conservatism and more realistic simulations of the physical phenomena. The challenge today is oriented toward the application of this technique to the operating conditions of nuclear research reactors. In the current study, a three-Dimensional Neutron Kinetics and best estimate Thermal-Hydraulic model based upon the coupled PARCS/RELAP5 codes has been developed and applied for a heavy water research reactor. The objective is to perform safety analysis related to design accidents of this reactor types. In the current study two positive reactivity insertion transients are considered, SCRAM protected and self-limiting power excursion cases. The results of the steady state calculations were compared with results obtained from conventional diffusion codes, while transient calculations were assessed using the point kinetic model of the RELAP5 code. Through this study, the applicability and the suitability of using the coupled code technique with respect to the classical models are emphasized and discussed.     

Startup and burnup strategy for Th–U/U–Pu fuel cycles in an EM2 reactor

General Atomics (GA) is developing the Energy Multiplier Module (EM²) which is a compact gas-cooled fast reactor as one of candidates of the Generation-IV nuclear energy systems. In the EM² core, low enriched uranium is used as igniting fuel and depleted uranium is used for converting and burning. It indicates that EM² can maintain critical operation for more than 30 years without refueling. To further study the Th–U fuel cycle performance in the EM², two kinds of start-up strategies with Th–U (Th + ²³³U) and semi Th–U (Th + enriched ²³⁵U) are evaluated. Neutronics characteristics, such as the effective multiplicity factor (k_eff) and conversion ratio (CR) are analyzed from neutron usage point of view. The simulated results for the two kinds of fuels are compared with the U–Pu fuel from the design of GA. The analysis gives an insight into the pros and cons of U–Pu and Th–U fuel cycles in terms of the breeding capability and the discharged radio-toxicity. The breeding performance of the second generation EM² is also presented and compared with that of the first generation EM². It indicates that the multi-generation EM² can deepen the burnup and reduce the waste management pressure for each kind of fuel loading strategy.